help please

Question

A Web music store offers two versions of a popular song. The size of the standard version is 2.5 megabytes (MB). The size of the high-quality version is 4.3 MB. Yesterday, there were 1130 downloads of the song, for a total download size of 4301 MB. How many downloads of the high-quality version were there?

Answer 1

n1 = number of standard version downloads

n2 = number of hq version downloads

s1 = the size of the standard version download

s2 - the size of the hq version download

 

System of equations:

Eq 1:  n1 + n2 = 1130

Eq 2:  n1*s1 + n2*s2 = 4301 MB

 

Solve Eq 1 for n1:

 

n1 = 1130 - n2

 

Substitute this into Eq 2:

 

(1130 - n2)*s1 + n2*s2 = 4301 MB

 

Solve for n2:

n2= (4301MB - 1130*s1)/(s2 - s1)

 

Substitute known values in and evaluate n2:

 

n2 = (4301 MB - 1130*2.5 MB)/(4.3 MB - 2.5 MB) = 820

 

Substitue n2 = 820 into Eq 1 and solve for n1:

 

n1 = 1130 - n2 = 1130 - 820 = 310

 

310 standard version downloads

820 high-quality version downloads